JP5535102B2 - Manufacturing method of metal separator material for fuel cell and metal separator material for fuel cell - Google Patents

Description

  The present invention relates to a method for producing a metal separator material for a fuel cell, which is formed by electroplating an Au coating layer on the surface of a stainless steel sheet, and a metal separator material for a fuel cell.

Solid polymer fuel cell separators have electrical conductivity, and each unit cell of the fuel cell is electrically connected to collect energy (electricity) generated in each unit cell and to each unit cell. A flow path for supplying fuel gas (fuel liquid) and air (oxygen) is formed. This separator is also called an interconnector, a bipolar plate, or a current collector.
Conventionally, a fuel cell separator having a gas flow path formed on a carbon plate has been used, but there is a problem that the material cost and processing cost are high. On the other hand, when a metal plate is used instead of the carbon plate, corrosion and elution become a problem because it is exposed to an oxidizing atmosphere at a high temperature. For this reason, the technology of coating the surface of the stainless steel plate with Au plating of 0.01 to 0.06 μm (Patent Document 1), the surface of the stainless steel plate with Au, Ru, Rh, Pd, Os, Ir, Pt, etc. A technique (Patent Document 2) for forming a conductive portion by sputtering a noble metal selected from the above is known.
In addition, a technique for performing gold plating directly in an acidic bath without applying a base treatment to the surface of a stainless steel sheet (Patent Document 3), or a technique for performing gold plating after forming an oxide film on the surface of a stainless steel sheet (Patent Document) 4) has been reported.
On the other hand, a technique (Patent Document 5) that performs high-speed plating with high current density by applying ultrasonic vibration to a plating bath has been reported.

JP-A-10-228914 JP 2001-297777 A JP 2004-296281 A JP 2007-257883 A JP 2002-256479 A

However, since gold is expensive, it is necessary to reduce the amount of gold used (gold film thickness), and it is necessary to perform thin (strike, 20 nm or less) gold plating directly on a stainless steel sheet. However, when the thickness of the gold plating is reduced to less than 20 nm, coating defects are likely to occur, and there is a problem that sufficient corrosion resistance of the fuel cell separator cannot be ensured. In particular, since the fuel cell separator is placed in an acidic atmosphere, it is in a severe environment in terms of corrosion resistance.
That is, an object of the present invention is to provide a method for producing a metal separator material for a fuel cell and a metal separator material for a fuel cell that are excellent in corrosion resistance even when the Au coating layer formed on the surface of the stainless steel thin plate is thin.

The method for producing a separator material for a fuel cell according to the present invention is for a fuel cell in which an Au coating layer having a thickness of 20 nm or less is formed on the surface of a substrate made of austenitic stainless steel sheet using an Au plating bath having a pH of 1.0 or less. In the method for producing a metal separator material, the surface roughness of the substrate is Ra ≦ 0.08 μm, and electrolytic plating is performed in a state where ultrasonic vibration is applied to the substrate and / or the Au plating bath.

The oscillation frequency of the ultrasonic vibration is preferably set to 25 to 60 kHz.
It is preferable that the Au coating layer is further sealed.
It is preferable to perform the sealing treatment by electrolytically treating the Au coating layer in a mercapto-based aqueous solution .

The separator material for a fuel cell of the present invention is produced by the method for producing a metal separator material for a fuel cell.
In the crystal grains of the base material, the arithmetic surface roughness (Ra) when the Au coating layer is measured with an atomic force microscope is preferably 3.0 nm or less.

  According to the present invention, the corrosion resistance can be improved even if the Au coating layer formed on the stainless steel sheet surface is thin.

The TEM image of the cross section of the separator material for fuel cells when the thickness of Au coating layer is 7 nm is shown. The TEM image of the cross section of the separator material for fuel cells when the thickness of Au coating layer is 15 nm is shown. It is sectional drawing of the fuel cell stack (single cell) which concerns on embodiment of this invention. 1 is a cross-sectional view of a planar fuel cell stack according to an embodiment of the present invention. It is a figure showing an example of the method of performing the manufacturing method of the metal separator material for fuel cells which concerns on embodiment of this invention, and showing a mode that a stainless steel strip passes the plating tank of a plating line. It is sectional drawing which shows the structure of a bipolar type separator.

Hereinafter, the manufacturing method of the metal separator material for fuel cells which concerns on embodiment of this invention is demonstrated. In the present invention, “%” means “% by mass” unless otherwise specified.
Further, in the present invention, the “metal separator for fuel cell” has electrical conductivity, electrically connects each single cell, collects energy (electricity) generated in each single cell, and collects each single cell. A fuel gas (fuel liquid) or air (oxygen) flow path to be supplied to the cell is formed. The separator is also referred to as an interconnector, a bipolar plate, or a current collector.
Therefore, as will be described in detail later, as a separator for a fuel cell, in addition to a separator having an uneven flow path on a plate-like substrate surface, a plate-like substrate surface such as the above-described passive DMFC separator is used. It includes a separator with gas and methanol passage holes.

<Base material>
Metal separator materials for fuel cells are required to have corrosion resistance and conductivity, and the base material is required to have corrosion resistance. For this reason, an austenitic stainless steel sheet having good corrosion resistance and relatively low cost is used as the base material.
The type of the austenitic stainless steel sheet is not particularly limited, and examples thereof include SUS201, SUS304, SUS304L, SUS304LN, SUS316, SUS316L, and SUSXM7, which are compliant with JIS. Here, SUS316L (stainless steel to which Mo is added by about 2.5%) is preferable in terms of excellent corrosion resistance.
The shape of the substrate is not particularly limited as long as it is a shape that can be plated with Au. However, the thickness of the thin plate is preferably 0.05 to 0.3 mm because it is press-formed into a separator shape.

Also, from the viewpoint of forming the Au coating layer smoothly, it is better to smooth the surface of the substrate. As surface finishing methods for stainless steel thin plates, BA (bright annealing), polishing finishing, and the like have been conventionally known. In the present invention for forming a thin Au coating layer of 20 nm or less, a BA-treated stainless steel thin plate is used. preferable.
Furthermore, when the surface roughness of the substrate is Ra ≦ 0.08 μm, it is preferable from the viewpoint of forming the Au coating layer smoothly. Since electrolytic plating tends to attach to the uneven surface of the base material surface, the surface roughness Ra of the base material is set to 0.08 μm or less so that plating is uniformly applied and defects such as pinholes can be reduced.

<Plating>
In order to electroplat the Au coating layer on the substrate surface, an Au plating bath having a pH of 1.0 or less is used. In order to directly plate Au on a stainless steel thin plate, the pH of the plating bath needs to be 1 or less. When an Au plating bath having a pH of 1.0 or less is used, the Cr oxide film on the surface of the stainless steel as a substrate is formed. It is easy to remove and the adhesion of the Au coating layer is improved.
In addition, plating adhesion is improved by directly (directly) Au plating on the surface of the substrate using an acidic Au plating bath. This is because, in the conventional connector materials, the Ni base plating is applied to the base material and then the Au plating is performed. However, since the acid resistance of Ni is weak, the Ni plating is peeled off by the atmosphere in the fuel cell. . Furthermore, since an acidic Au plating bath having a pH of 1.0 or less can be plated at a high current density, hydrogen is generated on the surface of the base material during the plating, the stainless steel surface is activated, and Au is easily attached.
On the other hand, when the pH of the Au plating bath exceeds 1.0, the plating adhesion to the substrate is lowered. If the pH of the Au plating bath is less than 0.2, excessive hydrogen is generated during electroplating and the plating current efficiency is lowered. Therefore, the pH is preferably 0.2 or more.
Examples of the Au plating bath having a pH of 1.0 or less include a bath mainly composed of sodium hydrogen sulfate and potassium gold cyanide. As the Au salt, a gold cyanide salt or the like can be used, and the gold concentration of the Au salt can be about 2 to 7 g / L.

As conditions for Au plating, when the current density is low, current concentrates on the convex portion of the substrate and the plating layer is difficult to flatten, and when the plating bath temperature is low, the plating layer tends to be difficult to flatten.
The gold concentration in the plating solution is preferably 1 to 4 g / L, more preferably 1 to 2 g / L. If the gold concentration is less than 1 g / L, the current efficiency tends to decrease and the plating layer tends not to be flat. The current density of Au plating is 1 to 8 A / dm ² , preferably 4 to 8 A / dm ² .

<Applying ultrasonic vibration>
In addition, when the Au plating thickness exceeds 20 nm, there is no problem. However, if the Au plating thickness is 20 nm or less, it is not sufficient to adjust the pH and bath composition of the Au plating bath described above, and the pinholes of the plating film increase and corrosion resistance is increased. descend. For this reason, ultrasonic wave irradiation is effective in Au plating with a thickness of 20 nm or less. The reason for this is that by using ultrasonic waves during Au plating, the Au plating bath is uniformly stirred and the gold ions in the bath are uniformly supplied to the surface of the substrate, so that pinholes can be reduced. Because. Further, cavitation is caused in the Au plating bath by ultrasonic waves, hydrogen and impurities staying on the surface of the base material are lifted, and plating defects (pinholes and the like) starting from these can be reduced.
The ultrasonic vibration may be applied to the base material and / or the Au plating bath. For example, the ultrasonic vibrator is brought into contact with the base material in the plating bath, or the ultrasonic vibrator is brought into contact with the Au plating bath. Thus, ultrasonic vibration can be applied. Moreover, although the stirring state and cavitation state of the Au plating bath change depending on the oscillation frequency of the ultrasonic vibration, when the frequency is 25 to 60 kHz, the effect of the ultrasonic wave can be stably exhibited.
As the ultrasonic vibrator, for example, a piezoelectric ceramic having titanium or hastelloy as an outer shell can be used.

<Au coating layer>
The thickness of the Au coating layer formed on the substrate surface (one side or both sides) is 20 nm or less from the viewpoint of cost, but is preferably 2 nm or more from the viewpoint of corrosion resistance and electrical characteristics (contact resistance between separator and MEA). When the thickness of the Au coating layer is preferably 5 to 20 nm, and more preferably 5 to 10 nm, the corrosion resistance is good and the cost can be reduced. The thickness of the Au coating layer can be calculated by an electrolytic method or a cross-sectional TEM (transmission electron microscope) image.
In the crystal grains of the substrate, the arithmetic surface roughness (Ra) of the Au coating layer measured with an atomic force microscope is preferably 3.0 nm or less. As a result of studies by the present inventors, it has been found that in a thin Au coating layer (thickness of 20 nm or less), the amount of metal elution from the substrate increases as the surface Ra increases. Although the cause of this is not clear, when the Au coating layer has a large Ra, electrodeposition is concentrated at a specific position on the substrate during electroplating, resulting in a portion with a thinner plating layer, resulting in film defects. It can be thought of that.
In addition, the electrodeposition state of Au on the substrate surface is different between the crystal grains of the substrate and the crystal grain boundaries. Specifically, since electrodeposition is concave at the grain boundary portion of the substrate, the measured value of Ra increases when the Ra of the portion including the grain boundary of the substrate is measured with an atomic force microscope (AFM). Therefore, in this invention, Ra measured in the crystal grain of a base material is employ | adopted as Ra of Au coating layer.
In addition, from the viewpoint of saving money, it is possible to apply Au plating only to the parts that require electrical conductivity, such as the parts that will be in contact with the electrodes when the fuel cell separator material is processed into a fuel cell separator. It is.

  FIG. 1 shows a TEM image of a cross section of a fuel cell separator material of Invention Example 1-3 described later. FIG. 2 shows a TEM image of a cross section of the fuel cell separator material of Invention Example 1-5 in the same manner.

When evaluating the smoothness of a thin and soft Au coating layer of 20 nm or less, it is difficult to evaluate nano level unevenness when measured with a contact-type surface roughness meter, and measuring the roughness of a substrate such as stainless steel turn into. Therefore, in the present invention, a non-contact atomic force microscope (AFM) is used for evaluating the smoothness of a thin Au layer.
When the Ra of the Au coating layer measured by AFM is 3.0 nm or less, the metal elution amount is greatly reduced. Although the Ra of the Au coating layer is preferably as small as possible, it is practically difficult to form a plating layer with an Ra of less than 0.5 nm.

  As a method for setting the Ra of the Au coating layer to 3.0 nm or less, sodium hydrogen sulfate is added as a conductive salt to the Au plating bath. In this case, as the composition of the Au plating bath, one containing Au salt, sodium hydrogen sulfate, and other additives as required can be used. Moreover, the density | concentration of sodium hydrogensulfate can be about 50-100 g / L.

In the bipolar separator shown in FIG. 6, it is preferable to change the plating thickness of the Au coating layer on the front and back surfaces. A fuel cell metal separator is generally manufactured by laminating two molded products obtained by press-molding a plate material of the above-described fuel cell metal separator material by laser welding or the like. Usually, cooling water is flowed to the back side of the metal separator material. On the other hand, the outer side of the separator (the surface side of the metal separator material for fuel cells) is in contact with a membrane electrode assembly (MEA) and a fuel gas or an oxidant gas is allowed to flow. Because it is used in this way, the surface side of the metal separator material for fuel cells is required to have high corrosion resistance, but the back side does not require so much corrosion resistance, so even if the Au plating thickness is made thinner than the surface side Good. Moreover, it is not necessary to carry out Au plating on the back surface side according to a use site | part and a use purpose.
In addition, Au plating may be performed only on a region corresponding to a portion (active area) that requires corrosion resistance in the separator, thereby reducing the amount of gold used (see FIG. 6).

<Sealing treatment>
The Au coating layer is preferably sealed. Even if a coating defect (pinhole part) exists in the Au coating layer, the defect can be filled by the sealing treatment, and the corrosion resistance can be maintained. Various methods are known for sealing the Au plating, but it is preferable to electrolyze the Au coating layer in a mercapto-based aqueous solution. The mercapto aqueous solution is obtained by dissolving a mercapto group-containing compound in water. Examples of the mercapto group-containing compound include mercaptobenzothiazole derivatives described in JP-A No. 2004-265695. Mercapto compounds are adsorbed and bonded to the pinholes to improve corrosion resistance.

<Separator for fuel cell>
Next, a fuel cell separator using the fuel cell separator material of the present invention will be described. As shown in FIG. 6, the fuel cell separator is formed by processing the above-described fuel cell separator material into a predetermined shape, such as fuel gas (hydrogen) or fuel liquid (methanol), air (oxygen), cooling water, etc. A reaction gas channel or a reaction liquid channel (groove or opening) for flow is formed.

<Laminated (active) fuel cell separator>
FIG. 3 is a cross-sectional view of a single cell of a stacked (active) fuel cell. In FIG. 3, current collector plates 140A and 140B are respectively arranged outside the separator 10 described later. Usually, when a stack is formed by stacking single cells, a pair of current collectors is provided only at both ends of the stack. A board is placed.
The separator 10 has electrical conductivity, has a current collecting action in contact with an MEA described later, and has a function of electrically connecting each single cell. Further, as will be described later, the separator 10 is formed with a groove serving as a flow path for fuel gas and air (oxygen).

  In FIG. 3, a membrane electrode assembly (MEA) 80 is configured by laminating an anode electrode 40 and a cathode electrode 60 on both sides of the solid polymer electrolyte membrane 20. An anode side gas diffusion film 90A and a cathode side gas diffusion film 90B are laminated on the surfaces of the anode electrode 40 and the cathode electrode 60, respectively. In the present invention, the membrane electrode assembly may be a laminate including the gas diffusion films 90A and 90B. For example, when a gas diffusion layer is formed on the surface of the anode electrode 40 or the cathode electrode 60, the laminated body of the solid polymer electrolyte membrane 20, the anode electrode 40, and the cathode electrode 60 is referred to as a membrane electrode assembly. May be.

On both sides of the MEA 80, the separator 10 is disposed so as to face the gas diffusion films 90A and 90B, respectively, and the separator 10 holds the MEA 80 therebetween. A flow path 10L is formed on the surface of the separator 10 on the MEA 80 side, and gas can enter and leave the interior space 20 surrounded by a gasket 12, a flow path 10L, and a gas diffusion film 90A (or 90B) described later. .
A fuel gas (hydrogen or the like) flows in the internal space 20 on the anode electrode 40 side, and an oxidizing gas (oxygen, air or the like) flows in the internal space 20 on the cathode electrode 60 side, so that an electrochemical reaction occurs. It has become.

The outer periphery of the periphery of the anode electrode 40 and the gas diffusion film 90 </ b> A is surrounded by a frame-shaped seal member 31 having substantially the same thickness as the laminated thickness. A substantially frame-shaped gasket 12 is interposed between the seal member 31 and the peripheral edge of the separator 10 so as to contact the separator, and the gasket 12 surrounds the flow path 10L. Furthermore, a current collector plate 140A (or 140B) is laminated on the outer surface of the separator 10 (the surface opposite to the MEA 80 side) in contact with the separator 10, and between the current collector plate 140A (or 140B) and the periphery of the separator 10 is stacked. A substantially frame-shaped sealing member 32 is interposed between the two.
The seal member 31 and the gasket 12 form a seal that prevents fuel gas or oxidizing gas from leaking out of the cell. When a plurality of single cells are stacked to form a stack, a gas different from the space 20 (when an oxidizing gas flows into the space 20) is formed in the space 21 between the outer surface of the separator 10 and the current collector plate 140A (or 140B). , Hydrogen flows in the space 21). Therefore, the seal member 32 is also used as a member for preventing gas from leaking outside the cell.

  The fuel cell is configured to include the MEA 80 (and the gas diffusion films 90A and 90B), the separator 10, the gasket 12, and the current collector plates 140A and 140B, and a fuel cell stack is configured by stacking a plurality of fuel cells. The

  The stacked (active) fuel cell shown in FIG. 3 can be applied not only to the above-described fuel cell using hydrogen as a fuel, but also to a DMFC using methanol as a fuel.

<Flat type (passive type) fuel cell separator>
FIG. 4 shows a cross-sectional view of a single cell of a planar (passive type) fuel cell. In FIG. 4, current collector plates 140 are arranged outside the separator 100. Normally, when a stack is formed by stacking single cells, a pair of current collector plates is arranged only at both ends of the stack. The
In FIG. 4, the configuration of the MEA 80 is the same as that of the fuel cell of FIG. 3, and thus the same reference numerals are given and description thereof is omitted (in FIG. 4, the description of the gas diffusion films 90 </ b> A and 90 </ b> B is omitted. Gas diffusion films 90A and 90B may be included).

In FIG. 4, the separator 100 has electrical conductivity, has a current collecting action in contact with the MEA, and has a function of electrically connecting each single cell. In addition, as will be described later, the separator 100 is formed with holes serving as fuel liquid and air (oxygen) flow paths.
The separator 100 is formed with a step portion 100s in the vicinity of the center of the long flat plate-like base material so that the cross section has a crank shape, an upper piece 100b positioned above the step portion 100s, and a step portion 100s. And a lower piece 100a located below. The step portion 100 s extends in a direction perpendicular to the longitudinal direction of the separator 100.
A plurality of separators 100 are arranged in the longitudinal direction, and a space is formed between the lower piece 100a and the upper piece 100b of the adjacent separators 100, and the MEA 80 is interposed in this space. A structure in which the MEA 80 is sandwiched between the two separators 100 is a single cell 300. In this way, a stack in which a plurality of MEAs 80 are connected in series via the separator 100 is configured.

  The planar (passive) fuel cell shown in FIG. 4 can be applied to a fuel cell using hydrogen as a fuel in addition to the DMFC using methanol as a fuel. Further, the shape and number of openings of the planar (passive type) fuel cell separator are not limited, and the openings may be slits in addition to the holes described above, or the entire separator may be net-like.

<Fuel cell stack>
The fuel cell stack of the present invention uses the fuel cell separator material of the present invention.
The fuel cell stack is formed by connecting a plurality of cells in which an electrolyte is sandwiched between a pair of electrodes, and a fuel cell separator is interposed between the cells to block fuel gas and air. The electrode in contact with the fuel gas (H ₂ ) is the fuel electrode (anode), and the electrode in contact with the air (O ₂ ) is the air electrode (cathode).
The configuration example of the fuel cell stack is as described with reference to FIGS. 3 and 4, but is not limited thereto.

<Preparation of sample>
Cold rolling and annealing were repeated on an austenitic stainless steel sheet having the composition shown in Table 1 (described in Table 1 in JIS standards) to obtain a base material having a thickness of 0.10 mm. In order to reduce the surface roughness, increase the surface cleanliness and suppress plating defects, the finish rolling uses a roll having a width of 450 mm controlled to a roll roughness Ra ≦ 0.08 μm, and suppresses surface oxidation. All annealing was performed in an atmosphere of 90% hydrogen or more. The surface roughness of the roll was measured according to JIS B 0601 using a stylus roughness meter (SJ-400 manufactured by Mitutoyo Corporation).

This substrate was subjected to electrolytic degreasing using a commercially available degreasing solution as a pretreatment, followed by washing with water, followed by electrolytic pickling and then washing with water. For electrolytic degreasing, a degreasing solution containing 40 g / L of sodium hydroxide and 5 g / L of a nonionic surfactant was used, and electrolysis was performed for 10 seconds using the substrate as a cathode. For the electrolytic pickling, an aqueous solution containing 50 g / L of sulfuric acid was used, and electrolysis was performed for 10 seconds using the base as a cathode.

Next, Au plating was directly performed on the base material after the pretreatment with a predetermined thickness (see Table 1) to produce a fuel cell separator material. Here, as shown in FIG. 5, an ultrasonic vibrator (made by Suntec Co., Ltd.) 4 having Hastelloy as the outer shell is disposed at the bottom of the Au plating tank 6, and the Au plating bath in the Au plating tank 6 is super Electrolytic plating was performed on the substrate 2 facing the anode 8 while applying sonic vibration. A seal structure 6a is provided on the side surface of the Au plating tank 6, and the base material 2 (stainless steel strip) is plated while passing through the side surface of the Au plating tank 6 through the seal structure 6a. .
The Au plating solution (cyanide) used was potassium gold cyanide (III) (gold concentration: 1 to 2 g / L) and sodium hydrogen sulfate 50 to 100 g / L, and the pH was changed as shown in Table 1. . The pH was adjusted by changing the amount of sodium hydrogen sulfate added. In the Au plating, there was no particular problem if the gold concentration in the plating bath was controlled within the range of 1 to 4 g / L and the current density of 1 to 8 A / dm ² .

  Further, some fuel cell separator materials (Invention Examples 3-1 and 3-2 in Table 1) were subjected to sealing after Au plating. Sealing treatment uses an aqueous solution containing 1 g / L of the sodium salt of mercaptobenzothiazole (Invention Example 3-1) and an aqueous solution containing 1 g / L of the sodium salt of benzotriazole (Invention Example 3-2). Electrolytic treatment was carried out for 10 seconds using the separator material for the anode as an anode.

  The arithmetic average roughness Ra and various characteristics of the surface of the fuel cell separator material produced as described above were measured as follows.

<Surface roughness>
The surface roughness Ra of the base material before plating is based on JIS B 0601, using a non-contact type three-dimensional measuring device (manufactured by Mitaka Kogyo Co., Ltd., model NH-3), with a cutoff of 0.25 mm and a measurement length of 1. The surface roughness Ra of the Au coating layer after plating, measured at 50 mm and n = 5, with the average value as the Ra value, was measured using an atomic force microscope (SPM-9600 manufactured by Shimadzu Corp.) (Non-contact method) With a scanning range of 1 μm × 1 μm, a scanning speed of 0.8 Hz, the location corresponding to the crystal grains of the base material before Au plating is measured at n = 3, and the average value is taken as the value of Ra Using.

<Adhesion of Au coating layer>
The Au plating material is bent at an angle of 90 degrees, then the bent part is returned to 0 degree, and the cellophane (registered trademark) is attached to the bent part and peeled off immediately, and the presence or absence of peeling of the Au coating layer is checked using an optical microscope. investigated. A tape having no Au coating layer attached to the tape was considered to have good adhesion (OK).

<Corrosion resistance>
The power generation performance (output, durability, etc.) of the fuel cell is better as the amount of ions eluted from the separator is smaller. In the corrosion resistance test simulating the power generation environment, the corrosion current density of the separator is 1.0 × 10 ^-5 (A / cm Less than ² ) is required. Accordingly, the corrosion current density of each fuel cell separator material was measured. The measurement is performed by immersing the test piece in a sulfuric acid solution at 90 ° C. and pH 3 with a potential of 0.8 V (SHE) applied to the test piece so as to simulate the power generation environment of the fuel cell, and the current flowing through the test piece after 20 hours. Was measured. And corrosion resistance was evaluated according to the following criteria. If the evaluation is A to B, there is no practical problem.
◎: Corrosion current density is less than 1 × 10 ^-7 (A / cm ² ) ○: Corrosion current density is 1 × 10 ^-7 (A / cm ² ) or more and less than 1 × 10 ^-6 (A / cm ² ) △: Corrosion current density is 1 × 10 ^-6 (A / cm ² ) or more and less than 1 × 10 ^-5 (A / cm ² ) ×: Corrosion current density is 1 × 10 ^-5 (A / cm ² ) or more

  The obtained results are shown in Table 1. Note that the front and back surfaces of the Au plating thickness in Table 1 correspond to the electrolyte membrane side (front surface) and the cooling water side (back surface) when assembled as a separator in a fuel cell, respectively. It was performed only on the surface of the battery separator material.

As is clear from Table 1, in the case of each of the examples in which the electroplating was performed using an Au plating bath having a pH of 1.0 or less and ultrasonic vibration was applied, the Au coating layer had a thickness of 20 nm or less. Excellent adhesion of the coating layer and excellent corrosion resistance.
Inventive Examples 2-1 and 2-4 in which the Au plating thickness and the pH of the plating bath are the same, Inventive Examples 2-1 and 2-2 in which the oscillation frequency of ultrasonic vibration is 25 and 60 kHz, respectively, The corrosion current density was smaller than that of the inventive examples, and the corrosion resistance and power generation performance were more excellent.
In the case of Invention Examples 3-1 and 3-2 in which sealing treatment was performed after Au plating, Invention Examples 1-4 and 1 where the Au plating thickness, the pH of the plating bath, and the oscillation frequency of ultrasonic vibration were the same. Compared to 8, the corrosion current density was small and the corrosion resistance was more excellent.
Moreover, also in the case of invention examples 4-1 to 4-3 in which the Au plating thicknesses were changed on the front and back of the base material, the corrosion resistance was excellent.

In addition, in the case of Invention Example 5-1, in which the base material is finish-rolled with a roll having a roll roughness Ra> 0.08 μm, and the surface roughness Ra of the base material also exceeds 0.08 μm, the other conditions are the same. Compared with Example 1-3, although the corrosion current density became large, there is no problem in practical use.
In the case of Invention Examples 6-1 and 6-2 in which the gold concentration in the Au plating bath is 4.5 g / L and 5.0 g / L, respectively, the gold concentration is 1 to 4 g / L, and other conditions are Although the corrosion current density is larger than that of the same Invention Example 1-4, there is no problem in practical use. Here, in Invention Example 6-2, the Ra of the Au coating layer exceeded 3.0 nm, and the corrosion current density increased.

On the other hand, in the case of Comparative Example 1-1 in which the pH of the Au plating bath exceeded 1.0, both the adhesion and corrosion resistance of the Au coating layer were inferior.
In the case of Comparative Example 1-2 in which Au plating was performed without applying ultrasonic vibration, the corrosion resistance was inferior.
Further, in Comparative Example 3-1, in which Au plating was performed without applying ultrasonic vibration and then sealing treatment was performed, the corrosion resistance was inferior.

2 Base Material 4 Ultrasonic Vibrator 6 Au Plating Tank 8 Anode 10, 100 Separator 12, 12B Gasket 20 Solid Polymer Electrolyte Membrane 40 Anode Electrode 60 Cathode Electrode 80 Membrane Electrode Assembly (MEA)

Claims (8)

A method for producing a metal separator material for a fuel cell , wherein an Au coating layer having a thickness of 20 nm or less is formed on a surface of a base material comprising an austenitic stainless steel thin plate using an Au plating bath having a pH of 1.0 or less , wherein The surface roughness of Ra ≦ 0.08 μm ,
A method for producing a metal separator material for a fuel cell, in which electrolytic plating is performed in a state where ultrasonic vibration is applied to the substrate and / or the Au plating bath.   The method for producing a metal separator for a fuel cell according to claim 1, wherein an oscillation frequency of the ultrasonic vibration is set to 25 to 60 kHz. The method for producing a metal separator material for a fuel cell according to claim 1 or 2, wherein the Au coating layer is further sealed.

  The method for producing a metal separator material for a fuel cell according to claim 3, wherein the sealing treatment is performed by subjecting the Au coating layer to electrolytic treatment in a mercapto-based aqueous solution.   The metal separator material for fuel cells manufactured by the manufacturing method of the metal separator material for fuel cells in any one of Claims 1-4. The metal separator material for a fuel cell according to claim 5, wherein an arithmetic surface roughness (Ra) when the Au coating layer is measured with an atomic force microscope is 3.0 nm or less in the crystal grains of the base material.   A fuel cell separator using the separator material according to claim 5.   A fuel cell stack using the fuel cell separator material according to claim 5.